linux-kernel - Re: [-next] !irqd_can_balance() WARNINGs at irq_move_masked

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Date:	Fri, 19 Jun 2015 22:11:46 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [-next] !irqd_can_balance() WARNINGs at irq_move_masked_irq()

On (06/19/15 14:21), Thomas Gleixner wrote:
> On Fri, 19 Jun 2015, Thomas Gleixner wrote:
> > On Fri, 19 Jun 2015, Sergey Senozhatsky wrote:
> > > [    0.412291] WARNING: CPU: 0 PID: 0 at kernel/irq/migration.c:21 irq_move_masked_irq+0x57/0xc4()
> > > [    0.412371] Can't balance irq 0 [edge]
> > 
> > Yuck.
> > 
> > > Do you guys want to replace WAN_ON() with WARN_ONCE(), perhaps? This, of course,
> > > doesn't fix anything; but at least one can boot the system. (not really a patch,
> > > just an idea).
> > 
> > Indeed. We really want to clear the move pending bit before the can
> > balance check. Patch below. But that does not explain why this happens
> > in the first place.
> > 
> > Can you please send me a full dmesg, kernel config and output of
> > /proc/interrupts ? (Private mail is fine, or upload it to some place)
> 
> Thanks for providing the data. I think I know what happens.
> 
> Something in the kernel (not yet clear what) tries to move the hpet
> irq 0 by calling irq_set_affinity(). That's an kernel internal
> interface which does not check whether the NO BALANCE flag is set for
> the irq. So the call runs and triggers the move from next interrupt
> machinery which ends up calling irq_move_masked_irq() and that trips
> over the flag and yells.
> 
> That's why I changed the WARN to a pr_warn() because we already know
> the call stack.
> 
> So the core behaviour is inconsistent. We let the caller of
> irq_set_affinity() succeed and yell later because we think it's wrong.
> 
> I'm pretty sure that we must drop the check for NO BALANCE in
> irq_move_masked_irq() and only check for the per_cpu bit, but at the
> same time I really want to know where that call to irq_set_affinity(irq0)
> is coming from.
> 
> Can you please collect the output of /proc/timer_list for the previous
> patch and then replace the previous patch with the one below and
> gather all the data again?
> 

It's 10pm here in Korea and I'm out of office already. I'll try
to collect the data tomorrow (or on Monday in the worst case).

Thank you.

	-ss
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